Structure of balance shaft

Abstract

A balance shaft structure for offsetting a secondary unbalance force due to a crankshaft of an engine may include a plurality of balance shafts rotating with the crankshaft, and a balance weight formed on a circumferential surface of each corresponding balance shaft and offsetting the secondary unbalance force, wherein the balance shafts may be disposed at the left and right of the crankshaft respectively and symmetric with respect to a longitudinal axis of the crankshaft, and disposed to be biased at a front part or a rear part of the engine, such that the center of weight may be offset by the center of weight of the engine, and a moment balance weight formed to each corresponding balance shaft and offsetting a pitch moment of the crankshaft generated by offsetting.

What is claimed is: 
     
         1 . A balance shaft structure for offsetting a secondary unbalance force due to a crankshaft of an engine, the structure comprising:
 a plurality of balance shafts rotating with the crankshaft; and   a balance weight formed on a circumferential surface of each corresponding balance shaft and offsetting the secondary unbalance force,   wherein the balance shafts are disposed at the left and right of the crankshaft respectively and symmetric with respect to a longitudinal axis of the crankshaft, and disposed to be biased at a front part or a rear part of the engine, such that the center of weight is offset by the center of weight of the engine, and   a moment balance weight formed to each corresponding balance shaft and offsetting a pitch moment of the crankshaft generated by offsetting.   
     
     
         2 . The structure of  claim 1 , wherein the plurality of balance shafts include first and second balance shafts disposed at both sides of the crankshaft, the first and second balance shafts having the same shape and being disposed on the same imaginary plane. 
     
     
         3 . The structure of  claim 1 ,
 wherein each moment balance weight includes a first moment balance weight and a second moment balance weight, and,   wherein the first moment balance weight and the second moment balance weight are disposed to have a phase difference of 180°.   
     
     
         4 . The structure of  claim 3 , wherein the first moment balance weight, the balance weight, and the second moment balance are disposed in series on corresponding balance shaft. 
     
     
         5 . The structure of  claim 3 , wherein the first moment balance weight and the balance weight are disposed to have the same phase angle. 
     
     
         6 . The structure of  claim 3 , wherein the first moment balance weight and the second moment balance weight are formed in disc shapes having a semicircular cross-section and a predetermined thickness. 
     
     
         7 . The structure of  claim 3 , wherein the first moment balance weight integrally extends from the balance weight and the second moment balance weight is disposed to have a phase difference of 180° from the first moment balance weight. 
     
     
         8 . The structure of  claim 7 , wherein the first moment balance weight and the second moment balance weight are formed in disc shapes having a semicircular cross-section and a predetermined thickness. 
     
     
         9 . The structure of  claim 1 , wherein the engine is an I4 engine. 
     
     
         10 . The structure of  claim 1 , wherein the balance shafts are driven at a double speed of the rotation speed of the crankshaft while having a phase difference of 180° from the crankshaft. 
     
     
         11 . The structure of  claim 1 , wherein the balance weight is a cylinder having a semicircular cross-section.